Flow Measurement Using NMR

Abstract

A nuclear magnetic resonance (NMR) method is used to determine a velocity distribution or velocity image of a flowing fluid in a downhole environment. The method comprises applying a radio frequency pulse sequence; applying a magnetic field gradient magnetic field and a gradient pulse duration; measuring a NMR signal; determining a phase characteristic of the NMR signal; and determining the velocity distribution or image of the fluid using the determined phase characteristic, the magnetic field gradient pulse parameters, and a time delay between gradient pulses.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority from and the benefit of U.S. Provisional Patent Application No. 60 / 877,946, filed Dec. 28, 2006.BACKGROUND OF INVENTION[0002]1. Field of the Invention[0003]The invention relates generally to flow measurement methods and systems. In particular, embodiments relate to flow measurements using Nuclear Magnetic Resonance (NMR) instruments.[0004]2. Background Art[0005]In industries where a flow of fluid is involved, measurements of flow parameters such as flow velocity and fluid viscosity are often required. Conventional flow measurement technologies include turbine flow meters and positive-displacement flow meters, both of which involve placement of moving parts in the flowing fluid. Moving pails, such as a turbine, disturb the flow pattern of the fluid, thus increasing the complexity of obtaining accurate measurements.[0006]Non-invasive (low measurements such as ultrasonic meters and NMR sensors have certain ad...

AI Technical Summary

Problems solved by technology

Moving pails, such as a turbine, disturb the flow pattern of the fluid, thus increasing the complexity of obtaining accurate measurements.

However, the FID signal is difficult to measure using permanent magnets because static magnetic field variations will result in signals that decay too fast for reliable detection.

Moreover, the King et al. methods for determining flow velocity do not account for the fact that there is a distribution of (low velocity in a pipe.

However, the computation requires prior knowledge of the fluid T1 distributions.

At higher flow velocities, the phase difference is no longer an adequate velocity indicator.

In contrast to a laminar flow, turbulent flow has a chaotic component and is much more difficult to model.

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